act the part

To behave in a way that is typical, befitting, or required of a particular role, occupation, etc. Look, we appointed you to be the manager of this department, so I suggest you start acting the part. He may dress like a successful lawyer, but he certainly doesn't act the part! If you want to be seriously considered for the full-time position at work, you need to act the part—come in on time, put your phone away, be attentive.